Which of the following process in urine formation is a non-selective?

(a) Reabsorption

(b) Secretion

(c) Filtration               

Filtration in urine formation is a non-selective process, meaning it occurs based on size rather than specific need. During filtration, blood from the body is delivered to the glomerulus through the afferent arteriole. The high pressure within the glomerulus forces water and solutes, including waste products and essential substances, to move from the blood within the capillaries into the Bowman's capsule. This process is driven by the hydrostatic pressure in the glomerulus and the relatively larger size of the capillary pores. Almost all small molecules in the blood, such as water, electrolytes, glucose, amino acids, and waste products like urea, are filtered through the glomerulus and into the Bowman's capsule. This initial filtrate, called "glomerular filtrate," is similar in composition to blood plasma.

After filtration, the next steps in urine formation involve more selective processes, such as reabsorption and secretion. Reabsorption involves the retrieval of essential substances (like glucose and water) and ions from the filtrate back into the blood. Secretion involves the active transport of additional waste products, excess ions, and other substances from the blood into the filtrate. These processes occur along the length of the renal tubules (proximal convoluted tubule, loop of Henle, distal convoluted tubule, and collecting duct) and are vital for maintaining the body's fluid and electrolyte balance.